A packaging paper for food has to fulfill many different and occasionally contradicting requirements. A first function of the packaging paper is that it protects the packaged food from environmental influences. This requires at least a certain mechanical strength and a chemical stability against typical environmental influences. A second function consists in that the packaging paper should also protect the environment from influences by the packaged food, with which it potentially comes into contact. For food this requires above all a sufficient resistance against the penetration of greases, oils and water through the packaging paper. Additionally the packaging paper for food should have a defined resistance against the penetration of water vapor, in order to prevent the food from drying out too quickly.
Because packaging paper for food is very often used only once, for ecological reasons it makes sense for the packaging paper to be recycled as easily as possible or, if it is not disposed of properly, that it can degrade biologically.
For the same reason, it is also desirable for the packaging paper for food to have a basis weight that is as low as possible, so that only a little raw material has to be used for the production and the amount of waste which is generated by the disposal of the packaging paper is comparatively small.
Typically, the requirements of a high or defined resistance against the penetration of greases and oils and good recyclability or biodegradability in combination with a low basis weight of the packaging paper contradict each other.
A process known in the state of the art for the production of packaging papers that achieves very good resistance against the penetration of greases, oils and water or water vapor consists in coating a base paper on one side with polyethylene, for example in an extrusion process. Because of this coating, such a paper cannot be recycled, or only with substantial effort. This process thus does not sufficiently fulfil the requirements of recyclability or biodegradability.
Another process known in the state of the art for the production of packaging papers that produces a very good resistance against the penetration of greases, oils and water consists in coating the paper with certain fluorine-containing substances. In particular, polyfluorinated organic compounds and above all fluorotelomer alcohols, CF3(CF2)n(CH2)mOH with n=1, 2, . . . , in particular with n=5 or n=7 and m=0, 1, 2, . . . , 10, in particular with m=0, 1 or 2, have been suitable for this application. The use of these substances, however, can lead to contamination with perfluorooctanoic acid (PFOA, C8HF15O2), which accumulates in the human organism and is rated as reproductively toxic, carcinogenic and toxic by the EU's REACH Regulations (Registration, Evaluation, Authorization of Chemicals). For this reason alone, polyfluorinated organic compounds are not desired as a component of a packaging paper and in particular not as a component of a packaging paper for food. Additionally, such papers are barely recyclable.
Many attempts to coat a packaging paper for food with substances of primarily biological origin so that, apart from good recyclability or biodegradability, a high resistance against the penetration of greases, oils and water can also be obtained, were not successful, because that resistance could not even come close to the high resistance against the penetration of greases, oils and water which is offered by a coating with polyethylene or polyfluorinated organic compounds, in particular not for packaging papers with a low basis weight.
In other experiments with a coating of the packaging paper with petroleum-based waxes, a high resistance against the penetration of greases, oils and water could be obtained, but the requirement for good recyclability or biodegradability was again only partially satisfied. In addition, these waxes based on petroleum products are ecologically disadvantageous.
A paper is described in WO 2015/180699 that contains nanoparticles of a biopolymer. These nanoparticles primarily increase the dry strength of the paper, so that a higher proportion of recycled fibers can be used, which provides ecological advantages. Furthermore, these nanoparticles increase the resistance against greases and oils. However, the papers described in this patent application are comparatively heavy, above 60 g/m2, and considerable amounts of nanoparticles are required, typically at least 6 g/m2, to obtain a sufficient strength. In addition, the use of perfluorooctanoic acid is still described as advantageous and despite all these measures, no resistance against greases or oils is obtained which exceeds a KIT level of 5.
Therefore, there is still a great need in the industry for a packaging paper to be available that has good strength and low raw material consumption, does not use organic fluorine compounds and nevertheless has a high resistance against greases and oils.